Surendra Singh Lilhore created HDFS-9355:
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             Summary: Support colocation in HDFS.
                 Key: HDFS-9355
                 URL: https://issues.apache.org/jira/browse/HDFS-9355
             Project: Hadoop HDFS
          Issue Type: New Feature
          Components: hdfs-client
            Reporter: Surendra Singh Lilhore
            Assignee: Surendra Singh Lilhore


Through this feature client can give suggestion to HDFS to write his all the 
blocks on same set of datanodes. Currently this we can achieve through 
HDFS-2576. HDFS-2576 give option to hint namenode about favored nodes, but in 
heterogeneous cluster this will not work out. Support client wants to write his 
data in directory which have COLD policy, but he don't know which DN have 
ARCHIVE storage, So he will not able to give favoredNodes list. 


*Implementation*

Colocation can enable by setting "dfs.colocation.enable" true in client 
configuration. If colocation is enable and  favoredNodes list is empty then 
{{DataStreamer}} will set first set of datanodes as favoredNodes which is 
chosen for first block and subsequent block will use the same datanodes for 
write. Before closing file client can get the favoredNodes list and same he can 
use for writing new file.
 



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